Diamine compound, polyimide precursor using same, and polyimide film

ABSTRACT

Disclosed is a novel diamine having a structure of comprising an intramolecular imide group, and further comprising aromatic cyclic groups linked by an ester group to both sides of the imide group. When the novel diamine is used as a polymerizable component for preparing a polyimide, a polyimide film having remarkably improved mechanical and thermal properties while maintaining optical properties can be provided.

This application is a 35 U.S.C. 371 National Phase Entry Applicationfrom PCT/KR2019/017841, filed on Dec. 17, 2019, designating the UnitedStates and claims the benefit of priorities to Korean Patent ApplicationNos. 10-2018-0163793 filed on Dec. 18, 2018 and 10-2019-0167742 filed onDec. 16, 2019, the entire disclosures of which are incorporated hereinby reference.

BACKGROUND OF THE INVENTION 1. Field of the Invention

The present invention relates to a novel diamine and a polyimideprecursor and a polyimide film by using the same.

In recent years, weight reduction and miniaturization of products havebeen emphasized in the field of display. A currently used glasssubstrate is heavy and brittle and is difficult to apply to a continuousprocess. Accordingly, researches are actively carried out for applying aplastic substrate having advantages of lightness, flexibility, andapplicability to continuous process and substitutable for a glasssubstrate, to a cell phone, a notebook and a PDA.

In particular, a polyimide (PI) resin has an advantage that it is easyto be synthesized, can be formed into a thin film and does not require acrosslinking group for curing. Recently, due to weight reduction andprecision of electronic products, a polyimide is widely used as amaterial for integration in semiconductor such as LCD, PDP, etc. Inparticular, many studies have progressed for PI to apply to a flexibleplastic display board having light and flexible characteristics.

A polyimide (PI) film, which is produced by film-forming the polyimideresin, is generally prepared by solution polymerization of aromaticdianhydride and aromatic diamine or aromatic diisocyanate to prepare asolution of polyamic acid derivative, coating the solution on a siliconwafer or a glass, and curing by heat treatment.

A flexible device involving a high temperature process requires heatresistance at high temperatures. In particular, an organic lightemitting diode (OLED) device manufactured using a low temperaturepolysilicon (LTPS) process may have a process temperature close to 500°C. However, at this temperature, thermal decomposition by hydrolysistends to occur even with the polyimide having excellent heat resistance.Therefore, in order to manufacture a flexible device, it is necessary tosecure excellent chemical resistance and storage stability so thatthermal decomposition by hydrolysis during the high temperature processdoes not occur.

In addition, the aromatic polyimide resin exhibits poor processabilityand brown coloring due to intramolecular interaction and charge transfercomplexation (CTC). To overcome this, attempts have been made tointroduce aliphatic chains, flexible linking groups, fluorinatedfunctional groups, and the like into monomers used in polyimideproduction. However, the introduction of these substituents caused aproblem of deteriorating the mechanical properties, which are strengthsof polyimide.

Accordingly, it is necessary to develop a technology capable ofimproving mechanical properties while maintaining the properties ofpolyimide.

BRIEF SUMMARY OF THE INVENTION

The present invention provides a novel diamine capable of producing apolyimide with improved physical properties.

The present invention also provides a polyimide precursor for producinga polyimide film with improved physical properties.

The present invention further provides a polyimide film prepared byusing the polyimide precursor.

The present invention also provides a flexible device comprising thepolyimide film and a process of manufacturing the same.

There is provided a diamine represented by the formula 1.

In the formula 1,

Z₁ to Z₈ are each independently a carbon atom or a nitrogen atom, withthe proviso that Z₁ to Z₈ are not nitrogen atoms at the same time, R₁,R₂, R₃ and R₄ are each independently selected from the group consistingof an alkyl group having 1 to carbon atoms, a haloalkyl group having 1to 10 carbon atoms, an alkenyl group having 1 to 10 carbon atoms, and anaryl group having 6 to 18 carbon atoms, n₁, n₂, n₃ and n₄ are eachindependently an integer of 0 to 4, and X is a single bond or afunctional group selected from the group consisting of O, S, S—S, C(═O),—C(═O)O—, CH(OH), S(═O)₂, Si(CH₃)₂, CR′R″, C(═O)NH and a combinationthereof, wherein R′ and R″ are each independently selected from thegroup consisting of a hydrogen atom, an alkyl group having 1 to 10carbon atoms and a fluoroalkyl group having 1 to carbon atoms.

According to one embodiment, in the formula 1, at least one of Z₁ to Z₄may be necessarily a carbon atom, and at least one of Z₅ to Z₈ may benecessarily a carbon atom.

According to one embodiment, in the formula 1, n₁ and n₂ may be eachindependently 0, or R₁ and R₂ may be each independently an alkyl grouphaving 1 to carbon atoms or a haloalkyl group having 1 to 5 carbonatoms.

According to one embodiment, in the formula 1, Z₁ to Z₄ may be allcarbon atoms.

According to one embodiment, in the formula 1, one of Z₁ to Z₄ may be anitrogen atom or one of Z₅ to Z₈ may be a nitrogen atom.

According to one embodiment, in the formula 1, one of Z₁ to Z₄ may be anitrogen atom and one of Z₅ to Z₈ may be a nitrogen atom.

According to one embodiment, in the formula 1, X may be selected from asingle bond, —O—, —CH₂—, —C(CF₃)—, —C(CH₃)₂—, or —SO₂—.

According to one embodiment, the diamine of the formula 1 may beselected from compounds of the formulas 1-1 to 1-20.

In addition, the present invention provides a polyimide precursorobtained by polymerizing a polymerization component comprising at leastone diamine and at least one acid dianhydride, wherein the diamine inthe polymerization component comprises the diamine represented by theformula 1.

In addition, the present invention provides a polyimide filmmanufactured by using the polyimide precursor.

According to one embodiment, the polyimide film may be manufactured by amethod comprising applying a polyimide precursor composition comprisingthe polyimide precursor on a carrier substrate; and heating and curingthe polyimide precursor composition.

In order to solve another problem of the present invention, there isprovided a flexible device comprising the polyimide film as a substrate.

In addition, the present invention provides a process for producing aflexible display comprising applying a polyimide precursor compositioncomprising the polyimide precursor on a carrier substrate; heating thepolyimide precursor composition to imidize polyamic acid, therebyforming a polyimide film; forming a device on the polyimide film; andpeeling off the polyimide film on which the device is formed from thecarrier substrate.

According to one embodiment, the process may comprise an LTPS (lowtemperature polysilicon) process, an ITO process or an oxide process.

In addition, the present invention provides a method for preparing adiamine having the structure of formula 1, the method comprising thesteps of:

reacting a compound of the formula (i) with a compound of the followingformula (ii) to obtain a compound of the formula (iii);

reacting the compound of the formula (iii) with a compound of theformula (iv) to obtain a compound of the formula (v); and

reducing the compound of the formula (v):

wherein,

Z_(a) to Z_(d) are each independently a carbon atom or a nitrogen atom,with the proviso that Z_(a) to Z_(d) are not nitrogen atoms at the sametime, R₁, R₂ and R_(a) are each independently selected from the groupconsisting of an alkyl group having 1 to 10 carbon atoms, a haloalkylgroup having 1 to 10 carbon atoms, an alkenyl group having 1 to 10carbon atoms, and an aryl group having 6 to 18 carbon atoms, n₁, n₂ andn are each independently an integer of 0 to 4, and X is a single bond ora functional group selected from the group consisting of O, S, S—S,C(═O), —C(═O)O—, CH(OH), S(═O)₂, Si(CH₃)₂, CR′R″, C(═O)NH and acombination thereof, wherein R′ and R″ are each independently selectedfrom the group consisting of a hydrogen atom, an alkyl group having 1 to10 carbon atoms and a fluoroalkyl group having 1 to carbon atoms.

The present invention discloses a novel diamine having a structurecomprising an intramolecular imide group and further comprising both ofimide groups having an aromatic ring group connected by an ester group,and can provide a polyimide film in which mechanical and thermalproperties are also significantly improved while maintaining opticalproperties when a novel diamine is used as a polymerization component inthe production of polyimide.

DETAILED DESCRIPTION OF THE INVENTION

Since various modifications and variations can be made in the presentinvention, particular embodiments are illustrated in the drawings andwill be described in detail in the detailed description. It should beunderstood, however, that the invention is not intended to be limited tothe particular embodiments, but includes all modifications, equivalents,and alternatives falling within the spirit and scope of the invention.In the following description of the present invention, detaileddescription of known functions will be omitted if it is determined thatit may obscure the gist of the present invention.

In the present specification, all compounds or organic groups may besubstituted or un-substituted, unless otherwise specified. Herein, theterm “substituted” means that at least one hydrogen contained in thecompound or the organic group is substituted with a substituent selectedfrom the group consisting of a halogen atom, an alkyl group or ahalogenated alkyl group having 1 to 10 carbon atoms, a cycloalkyl grouphaving 3 to 30 carbon atoms, an aryl group having 6 to 30 carbon atoms,a hydroxyl group, an alkoxy group having 1 to 10 carbon atoms, acarboxylic group, an aldehyde group, an epoxy group, a cyano group, anitro group, an amino group, a sulfonic group or a derivative thereof.

Aromatic polyimides are widely used in high-tech industries such asmicroelectronics, aerospace, insulating materials and refractorymaterials due to their excellent overall properties such as thermaloxidation stability, high mechanical strength, and excellent mechanicalstrength. However, aromatic polyimides having strong absorbance inultraviolet-visible region exhibit strong coloration from pale yellow todark brown. It limits their wide application in the optoelectronicsarea, where transparency and colorless properties are basicrequirements. The reason for the coloration in the aromatic polyimideresin is that intramolecular charge transfer complexes (CT-complexes)are formed between an alternating electron donor (dianhydride) and anelectron acceptor (diamine) in the polymer main chain.

To solve this problem, for the development of an optically transparentPI film having a high glass transition temperature (Tg), methods forintroducing functional groups, introducing bulky pendant groups,fluorinated functional groups, etc. into the polymer main chain, orintroducing flexible units (—S—, —O—, —CH₂—, etc.) have been studied.However, the introduction of these substituents may cause a problem ofdeteriorating the mechanical properties that are strengths of polyimide.

Therefore, the present invention provides a diamine represented by thefollowing formula 1 as a polymerization component capable of producing apolyimide with improved mechanical properties.

In the formula 1,

Z₁ to Z₈ are each independently a carbon atom or a nitrogen atom, withthe proviso that Z₁ to Z₈ are not nitrogen atoms at the same time,

R₁, R₂, R₃ and R₄ are each independently selected from the groupconsisting of an alkyl group having 1 to 10 carbon atoms, a haloalkylgroup having 1 to 10 carbon atoms, an alkenyl group having 1 to 10carbon atoms, and an aryl group having 6 to 18 carbon atoms,

n₁, n₂, n₃ and n₄ are each independently an integer of 0 to 4, and

X is a single bond or a functional group selected from the groupconsisting of O, S, S—S, C(═O), —C(═O)O—, CH(OH), S(═O)₂, Si(CH₃)₂,CR′R″, C(═O)NH and a combination thereof, wherein R′ and R″ are eachindependently selected from the group consisting of a hydrogen atom, analkyl group having 1 to 10 carbon atoms and a fluoroalkyl group having 1to 10 carbon atoms.

Since the diamine according to the present invention contains a diaminecontaining an imide group in a molecule, a charge transfer complexing(CTC) effect is increased through an increase in the interaction ofintermolecular pi-pi electrons of a diamine repeating unit containing animide group during polymerization of polyimide. As a result, themechanical properties are improved and the distance between molecules iscloser, so that the probability of the polymerization reaction increasesand thus the molecular weight can increase. In addition, due to astructure comprising both of imide groups connected by an aromatic ringgroup substituted with an ester group, the aromatic structures arecontinuously connected, so the elevated CTC effect is suppressed andprocessability is increased, and it enables intermolecular hydrogenbonding, so mechanical properties can be further improved. That is, theCTC effect can be suppressed again by the ester group, while improvingthe mechanical properties due to the elevated CTC effect by increasingthe imidization rate.

According to one embodiment, in the formula 1, Z₁ to Z₄ may be allcarbon atoms.

According to other embodiment, one of Z₁ to Z₄ may be a nitrogen atom orone of Z₅ to Z₈ may be a nitrogen atom, and according to otherembodiment, one of Z₁ to Z₄ may be a nitrogen atom and one of Z₅ to Z₈may be a nitrogen atom.

According to an embodiment, in the formula 1, n₁ and n₂ may be eachindependently 0, or R₁ and R₂ may be each independently an alkyl grouphaving 1 to carbon atoms or a haloalkyl group having 1 to 5 carbonatoms.

According to one embodiment, the diamine of the formula 1 may beprepared from the same reaction as in Scheme 1 below:

wherein Z_(a) to Z_(d) are each independently a carbon atom or anitrogen atom, with the proviso that Z_(a) to Z_(d) are not nitrogenatoms at the same time,

R₁, R₂ and R_(a) are each independently selected from the groupconsisting of an alkyl group having 1 to 10 carbon atoms, a haloalkylgroup having 1 to 10 carbon atoms, an alkenyl group having 1 to 10carbon atoms, and an aryl group having 6 to 18 carbon atoms, n₁, n₂ andn are an integer of 0 to 4, and

X is the same as defined in the formula 1.

In the step (1) of Scheme 1, the compound of formula (i) and thecompound of formula (ii) are reacted to obtain the compound of formula(iii).

The compound of formula (i) and the compound of formula (ii) may be usedin a molar ratio of 1:0.3 to 1:1, such as a molar ratio of 1:0.3 to1:0.7.

In the reaction of step (1), tetrahydrofuran (THF), ethyl acetate (EA),or the like may be used as an organic solvent, and propylene oxide maybe added as a catalyst to increase reactivity.

Further, in order to reduce the violent reaction due to high reactivity,the reaction is advantageously performed at 0° C., and the reaction timemay be 1 to 5 hours, such as 1 to 3 hours.

In the step (2) of Scheme 1, the compound of formula (iii) and thecompound of formula (iv) are reacted to obtain the compound of formula(v).

The compound of formula (iii) and the compound of formula (iv) may beused in a molar ratio of 1:0.3 to 1:1, such as a molar ratio of 1:0.3 to1:0.7.

In the reaction of step (2), acetic acid, propionic acid, etc. may beused to disperse the reaction compounds, and the reaction temperaturemay be raised to about 100° C. and the reaction time may be 3 to 5hours, such as 4 hours.

Subsequently, after lowering the reaction temperature to roomtemperature, alcohols such as ethanol and isopropanol may be added toobtain a solid.

In the step (3) of Scheme 1, the compound of formula (v) is reduced toobtain the compound of formula 1 finally.

The reduction reaction in step (3) may be carried out in a hydrogenatmosphere in the presence of a palladium on carbon (Pd/C) catalyst for12 to 18 hours, such as 16 hours. At this time, N-methylpyrrolidone,tetrahydrofuran, etc. may be used as a dispersion medium.

According to one embodiment, the weight average molecular weight of thepolyimide precursor prepared by using the diamine having the abovestructure may exceed 50,000 g/mol to improve mechanical properties. Forexample, it may have a weight average molecular weight of 51,000 to65,000 g/mol. When the molecular weight is 50,000 g/mol or less, theviscosity of the solution is lowered due to the decrease in polyimidereactivity, and the viscosity is low compared to the solid content, soit may not be easy to control the film thickness during the solutioncoating process and the final curing process. In addition, when themolecular weight is low, mechanical properties may be lowered, which maycause a problem that the film strength is lowered.

According to one embodiment, by including a nitrogen atom in thearomatic ring substituted with an ester group, the CTC effect can bereduced to improve the optical properties.

According to one embodiment, the diamine of the formula 1 may beselected from compounds of the formulas 1-1 to 1-20.

In the formula 1, a substituent including fluorine (F), for example, asubstituent such as a fluoroalkyl group, may reduce packing within astructure or between chains of polyimide, and may weaken electricalinteraction between chromogens due to steric hindrance and electricaleffects, resulting in high transparency in the visible region.

The polyimide precursor according to the present invention may comprisea diamine having the structure of formula 2 as a polymerizationcomponent:

In the formula 2,

R₅ and R₆ are each independently a monovalent organic group having 1 tocarbon atoms, and h is an integer of 3 to 200.

More specifically, the compound of formula 2 may be a diamine compoundof the following formula 2-1.

In the formula 2-1,

R is each independently an alkyl group having 1 to 10 carbon atoms or anaryl group having 6 to 24 carbon atoms, and

p and q are mole fractions, and when p+q=100, p is 70 to 90, and q is 10to 30.

The compound of formula 2 may be present in 5 to 50% by weight relativeto the total weight of the polymerization component, preferably 10 to20% by weight relative to the total weight of the total polymerizationcomponent.

When the polymerization component containing the structure of formula 2is excessively added relative to the total weight of the polymerizationcomponent, mechanical properties such as modulus of the polyimide may bedeteriorated and film strength may be reduced, resulting in physicaldamage such as tearing of the film during the process. In addition, whenthe diamine having the structure of formula 2 is excessively added, Tgderived from the polymer having the siloxane structure may appear, andas a result, Tg appears at a low process temperature of 350° C. orlower, and wrinkles may occur on the film surface due to the flowphenomenon of the polymer during the inorganic film deposition processof 350° C. or higher, resulting in cracks of the inorganic film.

In general, in the case of the polyimide containing 10% by weight ormore of the diamine comprising the silicone oligomer structure of theformula 2 in the polymerization component, the effect of reducingresidual stress may be increased, and in the case of higher than 50% byweight, Tg is lower than 390° C., so that heat resistance can belowered.

On the other hand, the polyimide according to the present invention canmaintain Tg of 390° C. or higher, despite containing a silicone oligomerin an amount of 10% by weight or more based on the total polymerizationcomponent. Therefore, while maintaining the glass transition temperatureat 390° C. or higher, the effect of reducing residual stress due to thesilicone oligomer structure can also be achieved.

The molecular weight of the silicone oligomer structure contained in thediamine having the structure of formula 2 may be 4000 g/mol or more,wherein the molecular weight means a weight average molecular weight,and the molecular weight may be calculated by using NMR analysis or anacid-base titration method to calculate the equivalent of the reactivegroup such as amine or dianhydride.

When the molecular weight of the silicone oligomer structure comprisingthe structure of formula 2 is less than 4000 g/mol, heat resistance maybe lowered, for example, the glass transition temperature (Tg) of theprepared polyimide may decrease, or the coefficient of thermal expansionmay increase excessively.

According to the present invention, the silicon oligomer domaindistributed in the polyimide matrix has a continuous phase, for examplethe size thereof is nano-sized, such as 1 nm to 50 nm, or 5 nm to 40 nm,or 10 nm to 30 nm, so that residual stress can be minimized whilemaintaining heat resistance and mechanical properties. If it does nothave such a continuous phase, there may be a residual stress reductioneffect, but it is difficult to use in the process due to a significantdecrease in heat resistance and mechanical properties.

Here, the domain of the silicone oligomer means a region in whichpolymers having a silicone oligomer structure are distributed, and itssize refers to a diameter of a circle surrounding the region.

It is preferable that the parts (domains) containing the siliconeoligomer structure are connected in a continuous phase in the polyimidematrix, wherein the continuous phase means a shape in which nano-sizeddomains are uniformly distributed.

Therefore, according to the present invention, despite having a highmolecular weight, the silicone oligomer can be uniformly distributed inthe polyimide matrix without phase separation, so that hazecharacteristics are lowered to obtain a polyimide having moretransparent characteristics. In addition, the presence of the siliconeoligomer structure in a continuous phase can improve mechanical strengthand stress relaxation effect of the polyimide more efficiently. Fromthese properties, the composition according to the present invention canprovide a flat polyimide film having improved thermal and opticalproperties by reducing bending of the substrate after coating-curing.

In the present invention, by inserting the silicone oligomer structureinto the polyimide structure, the modulus of the polyimide can beappropriately improved, and the stress caused by external force can alsobe relieved. The polyimide containing the silicone oligomer structuremay exhibit polarity, and phase separation may occur due to a polaritydifference with the polyimide structure that does not include thesiloxane structure, whereby the siloxane structure may be unevenlydistributed throughout the polyimide structure. In this case, it isdifficult to exhibit improvement effect of physical properties such asstrength improvement and stress relaxation of the polyimide due to thesiloxane structure, and haze increases due to phase separation, therebydeteriorating transparency of the film. Particularly, when the diaminecontaining the siloxane structure has a high molecular weight, thepolarity of the polyimide prepared therefrom may be more pronounced, sothat the phase separation phenomenon between the polyimides may be morepronounced. At this time, when using a siloxane diamine having a lowmolecular weight structure, a large amount of siloxane diamine must beadded in order to exhibit an effect such as stress relaxation. However,it may cause process problems such as a low Tg, and thus physicalproperties of the polyimide film may be deteriorated. Accordingly, inthe case that the siloxane diamine having a high molecular weight isadded, relaxation segments may be formed in the molecule largely, andthus a stress relaxation effect may be effectively exhibited even in asmall amount, compared to the case of adding a low molecular weight ofsiloxane diamine. Therefore, the present invention can be more evenlydistributed without phase separation in the polyimide matrix by usingthe compound of formula 2 having the siloxane structure with a highmolecular weight.

According to one embodiment, as the acid dianhydride used forpolymerizing the polyimide precursor, tetracarboxylic dianhydrides maybe used. For example, as the tetracarboxylic dianhydride, it may be useda tetracarboxylic dianhydride containing aliphatic, alicyclic oraromatic tetravalent organic group(s), or a combination thereof in themolecule, wherein the aliphatic, alicyclic or aromatic tetravalentorganic group(s) is connected to each other via a crosslinkingstructure. Preferably, it may include an acid dianhydride having astructure having a monocyclic or polycyclic aromatic, monocyclic orpolycyclic alicyclic group, or two or more of them connected by a singlebond or a functional group. Alternatively, it may include atetracarboxylic dianhydride comprising a tetravalent organic grouphaving aliphatic ring(s) or aromatic ring(s), in which each ring is asingle ring structure, each ring is fused to form a heterocyclicstructure, or each ring is connected by a single bond.

For example, it may include a tetracarboxylic dianhydride containing atetravalent organic group selected from structures of the followingformulas 3a to 3e.

In the formulas 3a to 3e,

R₁₁ to R₁₇ are each independently a substituent selected from a halogenatom selected from —F, —Cl, —Br and —I, a hydroxyl group (—OH), a thiolgroup (—SH), a nitro group (—NO₂), a cyano group, an alkyl group having1 to 10 carbon atoms, a halogenoalkoxy group having 1 to 4 carbon atoms,a halogenoalkyl group having 1 to 10 carbon atoms and an aryl grouphaving 6 to 20 carbon atoms,

a1 is an integer of 0 to 2, a2 is an integer of 0 to 4, a3 is an integerof 0 to 8, a4 and a5 are each independently an integer of 0 to 3, a6 anda9 are each independently an integer of 0 to 3, and a7 and a8 are eachindependently an integer of 0 to 7,

A₁₁ and A₁₂ are each independently selected from the group consisting ofa single bond, —O—, —CR′R″— (wherein, R′ and R″ are each independentlyselected from the group consisting of a hydrogen atom, an alkyl grouphaving 1 to 10 carbon atoms (e.g., methyl group, ethyl group, propylgroup, isopropyl group, n-butyl, tert-butyl group, pentyl group, etc.)and a haloalkyl group having 1 to 10 carbon atoms (e.g., trifluoromethylgroup, etc.)), —C(═O)—, —C(═O)O—, —C(═O)NH—, —S—, —SO—, —SO₂—,—O[CH₂CH₂O]y- (y is an integer of 1 to 44), —NH(C═O)NH—, —NH(C═O)O—, amonocyclic or polycyclic cycloalkylene group having 6 to 18 carbon atoms(e.g., cyclohexylene group, etc.), a monocyclic or polycyclic arylenegroup having 6 to 18 carbon atoms (e.g., phenylene group, naphthalenegroup, fluorenylene group, etc.), and combinations thereof.

Alternatively, the tetracarboxylic dianhydride may comprise atetravalent organic group selected from the group consisting of thefollowing formulas 4a to 4n.

At least one hydrogen atom in the tetravalent organic group of theformulas 4a to 4n may be substituted with a substituent selected from ahalogen atom selected from —F, —Cl, —Br and —I, a hydroxyl group (—OH),a thiol group (—SH), a nitro group (—NO₂), a cyano group, an alkyl grouphaving 1 to 10 carbon atoms, a halogenoalkoxy group having 1 to 4 carbonatoms, a halogenoalkyl group having 1 to 10 carbon atoms and an arylgroup having 6 to 20 carbon atoms. For example, the halogen atom may befluoro (—F), the halogenoalkyl group is a fluoroalkyl group having 1 to10 carbon atoms containing a fluoro atom, selected from a fluoromethylgroup, a perfluoroethyl group, a trifluoromethyl group, etc. The alkylgroup may be selected from a methyl group, an ethyl group, a propylgroup, an isopropyl group, a t-butyl group, a pentyl group, and a hexylgroup, and the aryl group is selected from a phenyl group and anaphthalenyl group. More preferably, it may be substituted with afluorine atom or a substituent containing a fluorine atom such as afluoroalkyl group.

Alternatively, the tetracarboxylic dianhydride may comprise atetravalent organic group comprising aliphatic ring(s) or aromaticring(s) in which each ring is a rigid structure, i.e., a single ringstructure, each ring is connected by a single bond, or each ring isdirectly connected to form a heterocyclic structure.

According to one embodiment, as the polymerization component of thepolyimide, one or more diamines may be further included in addition tothe diamine of formula 1. For example, it may include a diaminecomprising a divalent organic group selected from a monocyclic orpolycyclic aromatic divalent organic group having 6 to 24 carbon atoms,a monocyclic or polycyclic alicyclic divalent organic group having 6 to18 carbon atoms, or a divalent organic group having two or more of themconnected by a single bond or a functional group. Alternatively, it mayinclude a diamine comprising a divalent organic group having aliphaticring(s) or aromatic ring(s) in which each ring is a single ringstructure, each ring is fused to form a heterocyclic structure, or eachring is connected by a single bond.

For example, the diamine may comprise a divalent organic group selectedfrom the following formulas 5a to 5e.

In the formulas 5a to 5e,

R₂₁ to R₂₇ are each independently a substituent selected from a halogenatom selected from —F, —Cl, —Br and —I, a hydroxyl group (—OH), a thiolgroup (—SH), a nitro group (—NO₂), a cyano group, an alkyl group having1 to 10 carbon atoms, a halogenoalkoxy group having 1 to 4 carbon atoms,a halogenoalkyl group having 1 to 10 carbon atoms and an aryl grouphaving 6 to 20 carbon atoms,

A₂₁ and A₂₂ are each independently selected from the group consisting ofa single bond, —O—, —CR′R″— (wherein, R′ and R″ are each independentlyselected from the group consisting of a hydrogen atom, an alkyl grouphaving 1 to 10 carbon atoms (e.g., methyl group, ethyl group, propylgroup, isopropyl group, n-butyl, tert-butyl group, pentyl group, etc.)and a haloalkyl group having 1 to 10 carbon atoms (e.g., trifluoromethylgroup, etc.)), —C(═O)—, —C(═O)O—, —C(═O)NH—, —S—, —SO—, —SO₂—,—O[CH₂CH₂O]_(y)— (y is an integer of 1 to 44), —NH(C═O)NH—, —NH(C═O)O—,a monocyclic or polycyclic cycloalkylene group having 6 to 18 carbonatoms (e.g., cyclohexylene group, etc.), a monocyclic or polycyclicarylene group having 6 to 18 carbon atoms (e.g., phenylene group,naphthalene group, fluorenylene group, etc.), and combinations thereof,

b1 is an integer from 0 to 4, b2 is an integer from 0 to 6, b3 is aninteger from 0 to 3, b4 and b5 are each independently an integer from 0to 4, and b7 and b8 are each independently an integer from 0 to 9, andb6 and b9 are each independently an integer from 0 to 3.

For example, the diamine may comprise a divalent organic group selectedfrom the following formulas 6a to 6p.

Alternatively, the diamine may comprise a divalent organic group inwhich aromatic ring(s) or aliphatic structure(s) form a rigid chainstructure, for example, a divalent organic group having aliphaticring(s) or aromatic ring(s) in which each ring is a single ringstructure, each ring is connected by a single bond, or each ring isfused to form a heterocyclic structure.

According to one embodiment of the present invention, the reaction molarratio of the acid dianhydride to the diamine may be 1:1.1 to 1.1:1. Thereaction molar ratio may vary depending on the intended reactivity andprocessability. According to an embodiment of the present invention, themolar ratio of the acid dianhydride and the diamine may be 1:0.98 to0.98:1, preferably 1:0.99 to 0.99:1.

The reaction of acid dianhydride and diamine may be carried out by aconventional polymerization method of a polyimide or a precursorthereof, such as solution polymerization.

The organic solvent that can be used in the polymerization reaction ofpolyamic acid may include ketones such as gamma-butyrolactone,1,3-dimethyl-2-imidazolidinone, methyl ethyl ketone, cyclohexanone,cyclopentanone and 4-hydroxy-4-methyl-2-pentanone; aromatic hydrocarbonssuch as toluene, xylene and tetramethylbenzene; glycol ethers(Cellosolve) such as ethylene glycol monoethyl ether, ethylene glycolmonomethyl ether, ethylene glycol monobutyl ether, diethylene glycolmonoethyl ether, diethylene glycol monomethyl ether, diethylene glycolmonobutyl ether, propylene glycol monomethyl ether, propylene glycolmonoethyl ether, dipropylene glycol diethyl ether and triethylene glycolmonoethyl ether; ethyl acetate, butyl acetate, ethylene glycol monoethylether acetate, ethylene glycol monobutyl ether acetate, diethyleneglycol monoethyl ether acetate, dipropylene glycol monomethyl etheracetate, ethanol, propanol, ethylene glycol, propylene glycol, carbitol,dimethylpropionamide (DMPA), diethylpropionamide (DEPA),dimethylacetamide (DMAc), N,N-diethylacetamide, dimethylformamide (DMF),diethylformamide (DEF), N-methylpyrrolidone (NMP), N-ethylpyrrolidone(NEP), N,N-dimethylmethoxyacetamide, dimethylsulfoxide, pyridine,dimethylsulfone, hexamethylphosphoramide, tetramethylurea,N-methylcaprolactam, tetrahydrofuran, m-dioxane, p-dioxane,1,2-dimethoxyethane, bis(2-methoxyethyl)ether,1,2-bis(2-methoxyethoxy)ethane, bis[2-(2-methoxyethoxy)]ether, EquamideM100, Equamide B100 and the like, and these solvents may be used aloneor as a mixture of two or more.

According to one embodiment, as the organic solvent for polymerizing thepolymerization component, a solvent having a positive partitioncoefficient at 25° C. (Log P) may be used. By using an organic solventhaving a positive Log P, Tg can be maintained at a high temperature of390° C. or higher even for a composition in which methylphenylsiliconeoligomer is contained in an amount of 10% by weight or more.

The organic solvent having a positive partition coefficient as describedabove can reduce white turbidity generated by phase separation due topolarity difference between the flexible polyimide repeating structureand other polyimide structure comprising a siloxane structure such as asilicone oligomer. Conventionally, two kinds of organic solvents havebeen used in order to solve the phase separation problem. However, thepresent invention can reduce white turbidity due to phase separationeven with one kind of organic solvent, so that a more transparentpolyimide film can be produced.

There is a method in which a polar solvent and a non-polar solvent aremixed to solve the above problem. However, since a polar solvent hashigh volatility, it may be volatilized in advance during the productionprocess, which may cause problems such as deterioration of processreproducibility. In addition, the problem of phase separation cannot becompletely solved, resulting in high haze and low transparency of theproduced polyimide film.

More specifically, by using a solvent of which the molecules have anamphiphilic structure, it is possible to solve the process problem dueto the use of a polar solvent. Moreover, owing to the amphiphilicmolecular structure, the polyimide can be evenly distributed even ifonly a solvent is used, which makes it very suitable for solvingproblems caused by phase separation. Accordingly, it is possible toprovide a polyimide in which haze characteristics are significantlyimproved.

The solvent has a positive partition coefficient value means that thepolarity of the solvent is hydrophobic. According to the research of thepresent inventors, it is found that when the polyimide precursorcomposition is prepared using a specific solvent having a positivepartition coefficient value, the edge back phenomenon is improved. Inaddition, in the present invention it is possible to control the edgeback phenomenon of the solution without using additives for controllingsurface tension of the material and smoothness of the coating film, suchas a leveling agent, by using a solvent having a positive Log P asdescribed above. Since additional additives such as additives are notused, it is possible to eliminate quality and process problems such asthe presence of low-molecular substances in the final product, as wellas more efficiently to form a polyimide film having uniform properties.

For example, in the process of coating the polyimide precursorcomposition on the glass substrate, an edge back phenomenon may occurdue to shrinkage of the coating layer during curing or under thecondition of standing the coating solution in a humidity condition. Theedge back phenomenon of the coating solution may cause a variation inthe thickness of the film. As a result, the film may be cut or edges ofthe film may be broken when cutting due to a lack of flex resistance ofthe film, causing problems of poor process workability and reducedyield.

In addition, when fine foreign substances having polarity are introducedinto the polyimide precursor composition applied on the substrate, forthe polyimide precursor composition including a polar solvent having anegative Log P, sporadic coating cracks or thickness change may occurbased on location of the foreign substance due to polarity of theforeign substance. In case of using a hydrophobic solvent having apositive Log P, the occurrence of thickness change due to cracking ofthe coating may be reduced or suppressed even when fine foreignsubstances having polarity are introduced.

Specifically, in the polyimide precursor composition including a solventhaving a positive Log P, an edge back ratio defined by the followingEquation 1 may be 0% to 0.1% or less.

Edge back ratio (%)=[(A−B)/A]×100  [Equation 1]

wherein,

A: area of the polyimide precursor composition completely coated on thesubstrate (100 mm×100 mm),

B: area after the edge back phenomenon occurs from the edge of thesubstrate with the polyimide precursor composition or the PI film coatedthereon.

The edge back phenomenon of the polyimide precursor composition and thefilm may occur within 30 minutes after coating the polyimide precursorcomposition solution, in particular, the film may be rolled up from theedge to make the thickness of the edge thicker.

After coating the polyimide precursor composition according to thepresent invention on a substrate and then standing in a humiditycondition for 10 minutes or more, for example 10 minutes or more, forexample, 40 minutes or more, the edge back ratio of the coated resincomposition solution may be 0.1% or less. For example, even afterstanding at a temperature of 20 to 30° C. and in a humidity condition of40% or more, more specifically, in a humidity condition in the range of40% to 80%, that is, in each humidity condition of 40%, 50%, 60%, 70%,80%, for example in a humidity condition of 50% for 10 to 50 minutes,the edge back ratio may be 0.1% or less, preferable 0.05%, morepreferably almost 0%.

After coating the polyimide precursor composition on a substrate andthen standing at a temperature of 20 to 30° C. and in a humiditycondition of 40% or more, more specifically, in a humidity condition inthe range of 40% to 80%, that is, in each humidity condition of 40%,50%, 60%, 70%, 80%, for example in a humidity condition of 50% for 10 to50 minutes, the edge back ratio as described above is maintained evenafter curing, for example, the edge back ratio of the coated resincomposition solution is 0.1% or less. That is, even in a curing processby heat treatment, there may be little or no edge back phenomenon, andspecifically the edge back ratio may be 0.05% or less, more preferablyalmost 0%.

By solving this edge back phenomenon, the polyimide precursorcomposition according to the present invention can obtain a polyimidefilm having more uniform characteristics, thereby further improving theyield of the manufacturing process.

In addition, the density of the solvent according to the presentinvention can be 1 g/cm³ or less as measured by standard ASTM D1475. Ifthe density is more than 1 g/cm³, the relative viscosity may increaseand the process efficiency may be reduced.

The solvent having a positive partition coefficient (Log P) may be atleast one selected from the group consisting of N,N-diethylacetamide(DEAc), N,N-diethylformamide (DEF), N-ethylpyrrolidone (NEP),dimethylpropionamide (DMPA) and diethylpropionamide (DEPA).

The solvent may have a boiling point of 300° C. or less. Morespecifically, the partition coefficient Log P at 25° C. may be 0.01 to3, or 0.01 to 2, or 0.1 to 2.

The partition coefficient can be calculated using an ACD/Log P module ofACD/Percepta platform from ACD/Labs. The ACD/Log P module uses analgorithm based on QSPR (Quantitative Structure-Property Relationship)methodology using 2D molecular structures.

In addition, aromatic hydrocarbons such as xylene and toluene may befurther used. In order to facilitate dissolution of the polymer, about50% by weight or less of an alkali metal salt or an alkaline earth metalsalt may be further added to the solvent based on the total amount ofthe solvent.

In addition, in the case of synthesizing polyamic acid or polyimide, anend-capping agent may be further added in which the terminal of themolecule reacts with dicarboxylic acid anhydride or monoamine to end-capthe terminal of the polyimide in order to inactivate excess polyaminogroups or acid anhydride groups.

The reaction of tetracarboxylic dianhydride and diamine may be carriedout by a conventional polymerization method of polyimide precursor, suchas solution polymerization. Specifically, it can be prepared bydissolving diamine in an organic solvent, followed by addingtetracarboxylic dianhydride to the resulting mixed solution topolymerize.

The polymerization reaction may be carried out in an inert gas or anitrogen stream and may be carried out under anhydrous condition.

The reaction temperature during the polymerization reaction may be −20to 80° C., preferably 0 to 80° C. If the reaction temperature is toohigh, the reactivity may become high and the molecular weight may becomelarge, and the viscosity of the precursor composition may increase,which may be unfavorable in the process.

It is preferable that the polyamic acid solution prepared according tothe above-mentioned manufacturing method contains a solid content in anamount such that the composition has an appropriate viscosity inconsideration of processability such as coating property in the filmforming process.

The polyimide precursor composition containing polyamic acid may be inthe form of a solution dissolved in an organic solvent. For example,when the polyimide precursor is synthesized in an organic solvent, thesolution may be the reaction solution as obtained, or may be obtained bydiluting this reaction solution with another solvent. When the polyimideprecursor is obtained as a solid powder, it may be dissolved in anorganic solvent to prepare a solution.

According to one embodiment, the content of the composition may beadjusted by adding an organic solvent such that the total polyimideprecursor content is 8 to 25% by weight, preferably 10 to 25% by weight,more preferably 10 to 20% by weight.

The polyimide precursor composition may be adjusted to have a viscosityof 3,000 cP or more at a solid content concentration of 20% by weight orless, and the polyimide precursor composition may be adjusted to have aviscosity of 10,000 cP or less, preferably 9,000 cP or less, morepreferably 8,000 cP or less. When the viscosity of the polyimideprecursor composition is greater than 10,000 cP, the efficiency ofdefoaming during processing of the polyimide film is lowered. It resultsin not only the lowered efficiency of process but also the deterioratedsurface roughness of the produced film due to bubble generation. It maylead to the deteriorated electrical, optical and mechanical properties.

Then, the polyimide precursor resulted from the polymerization reactionmay be imidized by chemical or thermal imidization to prepare atransparent polyimide film.

According to one embodiment, the polyimide film may be manufactured by amethod comprising:

applying the polyimide precursor composition onto a substrate; and

heating and curing the applied polyimide precursor composition.

As the substrate, a glass substrate, a metal substrate, a plasticsubstrate, or the like can be used without any particular limitation.Among them, a glass substrate may be preferable which is excellent inthermal and chemical stabilities during the imidization and curingprocess for the polyimide precursor and can be easily separated evenwithout any treatment with additional release agent while not damagingthe polyimide film formed after curing.

The applying process may be carried out according to a conventionalapplication method. Specifically, a spin coating method, a bar coatingmethod, a roll coating method, an air knife method, a gravure method, areverse roll method, a kiss roll method, a doctor blade method, a spraymethod, a dipping method, a brushing method, or the like may be used. Ofthese, it is more preferable to carry out by a casting method whichallows a continuous process and enables to increase an imidization rateof polyimide.

In addition, the polyimide precursor composition may be applied on thesubstrate in the thickness range such that the polyimide film to befinally produced has a thickness suitable for a display substrate.

Specifically, it may be applied in an amount such that the thickness is10 to 30 μm. After the application of the polyimide precursorcomposition, a drying process for removing the solvent remained in thepolyimide precursor composition may be further optionally performedprior to the curing process.

The drying process may be carried out according to a conventionalmethod. Specifically, the drying process may be carried out at atemperature of 140° C. or lower, or from 80° C. to 140° C. If the dryingtemperature is lower than 80° C., the drying process becomes longer. Ifthe drying temperature exceeds 140° C., the imidization proceedsrapidly, making it difficult to form a polyimide film having a uniformthickness.

Then, the polyimide precursor composition is applied on a substrate andheat-treated in an IR oven, in a hot air oven, or on a hot plate. Theheat treatment temperature may range from 300 to 500° C., preferablyfrom 320 to 480° C. The heat treatment may be performed in a multi-stepheating process within the above temperature range. The heat treatmentprocess may be performed for 20 to 70 minutes, and preferably for 20 to60 minutes.

The residual stress immediately after curing of the polyimide filmprepared as described above may be 40 MPa or less, and the residualstress change after standing the polyimide film at 25° C. and 50%humidity for 3 hours may be 5 MPa or less.

The polyimide film may have a yellowness of 15 or less, and preferably13 or less. Further, the polyimide film may have a haze of 2 or less,and preferably 1 or less.

In addition, the polyimide film may have a transmittance at 450 nm of75% or more, a transmittance at 550 nm of 85% or more, and atransmittance at 630 nm of 90% or more.

The polyimide film may have high heat resistance, for example, a thermaldecomposition temperature (Td_1%) in which mass loss is 1% may be 500°C. or higher.

The polyimide film prepared as described above may have a modulus of 3to 6 GPa. When the modulus (modulus of elasticity) is less than 3 GPa,the film has a low rigidity and is easily fragile to external impact.When the modulus of elasticity exceeds 6 GPa, the rigidity of thecoverlay film is excellent, but sufficient flexibility cannot beobtained.

In addition, the polyimide film may have an elongation of 90% or more,preferably 91% or more, and a tensile strength of 130 MPa or more,preferably 138 MPa or more.

In addition, the polyimide film according to the present invention mayhave excellent thermal stability against a temperature change. Forexample, it may have a thermal expansion coefficient of −10 to 100 ppm/°C., preferably from −7 to 90 ppm/° C., more preferably 80 ppm/° C. orless, after the n+1 times heating and cooling processes in a temperaturerange of 100 to 350° C. times (n is an integer of at least 0).

In addition, the polyimide film according to the present invention mayhave a retardation in a thickness direction (R_(th)) of −150 nm to +150nm, preferably −130 nm to +130 nm, thereby exhibiting optical isotropyto improve visual sensibility.

According to one embodiment, the polyimide film may have an adhesiveforce to a carrier substrate of 5 gf/in or more, and preferably 10 gf/inor more.

In addition, the present invention provides a process for manufacturinga flexible device, comprising the steps of:

preparing a polyimide precursor composition;

applying the polyimide precursor composition on a carrier substrate, andthen heating to imidize the polyamic acid, thereby forming a polyimidefilm;

forming a device on the polyimide film; and

peeling from the carrier substrate the polyimide film having the deviceformed thereon.

In particular, the process of manufacturing a flexible device maycomprise a low temperature polysilicon (LTPS) process, an ITO process,or an oxide process.

For example, a flexible device including an LTPS layer may be obtainedby forming the LTPS layer by an LTPS thin film manufacturing process,followed by peeling a carrier substrate and a polyimide film by laserlift-off or the like, the LTPS thin film manufacturing processcomprising:

forming a barrier layer comprising SiO₂ on the polyimide film;

depositing an a-Si (amorphous silicon) thin film on the barrier layer;

dehydrogen annealing by thermal treating the deposited a-Si thin film ata temperature of 450° C.±50° C.; and

crystallizing the a-Si thin film with an excimer laser or the like.

The oxide thin film process may be heat treated at a lower temperaturethan the process using silicon, for example, the heat treatmenttemperature of the ITO TFT process may be 240° C.±50° C., and the heattreatment temperature of the oxide TFT process may be 350° C.±50° C.

Hereinafter, embodiments of the present invention will be described indetail so that those skilled in the art can easily carry out the presentinvention. The present invention may, however, be embodied in manydifferent forms and should not be construed as limited to theembodiments set forth herein.

<Preparative Example 1> Preparation of Compound of Formula 1-1

The compound of Formula A (35.0 g, 166.7 mmol) was dissolved in THE (270mL) in a nitrogen atmosphere, and pyridine (pyr) (26.4 g, 333.4 mmol)was added, followed by cooling to 0° C. The compound of formula B (11.6g, 83.4 mmol) was introduced into this solution in 4 portions atintervals of 10 minutes. After 3 hours, hexane (270 mL) was added toproduce a solid. The solid obtained after filtration was washed withhexane/ethyl acetate (10/7) to prepare the compound of formula C (23.8g, yield 91.3%).

MS [M+H]⁺=314

The compound of formula C (20 g, 63.9 mmol) and a compound of formula D(10.2 g, 32.0 mmol) were dispersed in glacial acetic acid (200 mL) andheated to 100° C. After 4 hours, the temperature was lowered to roomtemperature, and then ethanol was added to obtain a solid. The solidobtained after filtration was washed with water and ethanol to preparethe compound of formula E (25.9 g, yield 88.8%).

MS [M+H]⁺=911

After dispersing the compound of formula E (20 g, 22.0 mmol) in NMP(N-methylpyrrolidone) (180 mL), palladium on carbon (Pd/C) (0.60 g) wasadded and stirred in a hydrogen atmosphere for 16 hours. After thecompletion of the reaction, water (180 mL) was added to the filtrateobtained after filtration to produce a solid. The solid obtained afterfiltration was recrystallized from NMP and ethyl acetate to prepare thecompound of formula 1-1 (14.8 g, yield 79.9%).

MS [M+H]⁺=851

<Preparative Example 2> Preparation of Compound of Formula 1-2

A compound of formula G was prepared in the same manner as the method ofpreparing the compound of formula C, except that a compound of formula Fwas used instead of the compound of formula B in Preparation Example 1.

A compound of formula H was prepared in the same manner as the method ofpreparing the compound of formula E, except that the compound of formulaG was used instead of the compound of formula C. Finally, a compound offormula 1-2 was prepared in the same manner as the method of preparingthe compound of formula 1-1, except that the compound of formula H wasused instead of the compound of formula E.

MS [M+H]⁺=853

<Preparative Example 3> Preparation of Compound of Formula 1-9

A compound of formula J was prepared in the same manner as the method ofpreparing the compound of formula E, except that a compound of formula Iwas used instead of the compound of formula D in Preparation Example 1.

A compound of formula 1-9 was prepared in the same manner as the methodof preparing the compound of formula 1-1, except that the compound offormula J was used instead of the compound of formula E.

MS [M+H]⁺=731

<Preparative Example 4> Preparation of Compound of Formula 1-10

A compound of formula G was prepared in the same manner as the method ofpreparing the compound of formula C, except that a compound of formula Fwas used instead of the compound of formula B in Preparation Example 1.

A compound of formula K was prepared in the same manner as the method ofpreparing the compound of formula E, except that the compound of formulaG was used instead of the compound of formula C and the compound offormula I was used instead of the compound of formula D. Finally, acompound of formula 1-10 was prepared in the same manner as the methodof preparing the compound of formula 1-1, except that the compound offormula K was used instead of the compound of formula E.

MS [M+H]⁺=733

<Preparative Example 5> Preparation of Compound of Formula 1-13

A compound of formula M was prepared in the same manner as the method ofpreparing the compound of formula C, except that a compound of formula Lwas used instead of the compound of formula B in Preparation Example 1.

A compound of formula O was prepared in the same manner as the method ofpreparing the compound of formula E, except that the compound of formulaM was used instead of the compound of formula C and the compound offormula N was used instead of the compound of formula D.

Finally, a compound of formula 1-13 was prepared in the same manner asthe method of preparing the compound of formula 1-1, except the compoundof formula O was used instead of the compound of formula E.

MS [M+H]⁺=731

<Preparative Example 6> Preparation of Compound of Formula 1-14

A compound of formula Q was prepared in the same manner as the method ofpreparing the compound of formula C, except that a compound of formula Pwas used instead of the compound of formula B in Preparation Example 1.

A compound of formula R was prepared in the same manner as the method ofpreparing the compound of formula E, except that the compound of formulaQ was used instead of the compound of formula C and the compound offormula N was used instead of the compound of formula D.

Finally, a compound of formula 1-14 was prepared in the same manner asthe method of preparing the compound of formula 1-1, except that thecompound of formula R was used instead of the compound of formula E.

MS [M+H]⁺=733

<Preparative Example 7> Preparation of Compound of Formula 1-15

A compound of formula M was prepared in the same manner as the method ofpreparing the compound of formula C, except that a compound of formula Lwas used instead of the compound of formula B in Preparation Example 1.

A compound of formula T was prepared in the same manner as the method ofpreparing the compound of formula E, except that the compound of formulaM was used instead of the compound of formula C and the compound offormula S was used instead of the compound of formula D.

Finally, a compound of formula 1-15 was prepared in the same manner asthe method of preparing the compound of formula 1-1, except that thecompound of formula T was used instead of the compound of formula E.

MS [M+H]⁺=867

<Preparative Example 8> Preparation of Compound of Formula 1-16

A compound of formula Q was prepared in the same manner as the method ofpreparing the compound of formula C, except that a compound of formula Pwas used instead of the compound of formula B in Preparation Example 1.

A compound of formula U was prepared in the same manner as the method ofpreparing the compound of formula E, except that the compound of formulaQ was used instead of the compound of formula C and the compound offormula S was used instead of the compound of formula D.

Finally, a compound of formula 1-16 was prepared in the same manner asthe method of preparing the compound of formula 1-1, except that thecompound of formula U was used instead of the compound of formula E.

MS [M+H]⁺=869

<Comparative Example 1> 6-FDA/TFMB

130 g of DEAc (Diethylacetamide) was charged into a reactor in anitrogen stream, and then 0.0500 mol of TFMB(2,2′-Bis(trifluoromethyl)benzidine) was added to dissolve it whilemaintaining the reactor temperature at 25° C. To the solution with TFMBadded, 0.0500 mol of 6-FDA (4,4′-(Hexafluoroisopropylidene)diphthalicanhydride) and 40 g of DEAc were added and reacted for 48 hours toobtain a polyimide precursor solution.

<Example 1> 6-FDA/Diamine of Formula 1-1

200 g of DEAc (Diethylacetamide) was charged into a reactor in anitrogen stream, and then 0.0413 mol of the diamine of formula 1-1prepared in Preparative Example 1 was added to dissolve it whilemaintaining the reactor temperature at 25° C. To the solution with thediamine of formula 1-1 added, 0.0413 mol of 6-FDA(4,4′-(Hexafluoroisopropylidene)diphthalic anhydride) and 60 g of DEAcwere added and reacted for 48 hours to obtain a polyimide precursorsolution.

<Example 2> 6-FDA/Diamine of Formula 1-2

200 g of DEAc (Diethylacetamide) was charged into a reactor in anitrogen stream, and then 0.0413 mol of the diamine of formula 1-2prepared in Preparative Example 2 was added to dissolve it whilemaintaining the reactor temperature at 25° C. To the solution with thediamine of formula 1-2 added, 0.0413 mol of 6-FDA(4,4′-(Hexafluoroisopropylidene)diphthalic anhydride) and 60 g of DEAcwere added and reacted for 48 hours to obtain a polyimide precursorsolution.

<Example 3> 6-FDA/Diamine of Formula 1-9

180 g of DEAc (Diethylacetamide) was charged into a reactor in anitrogen stream, and then 0.0413 mol of the diamine of formula 1-9prepared in Preparative Example 3 was added to dissolve it whilemaintaining the reactor temperature at 25° C. To the solution with thediamine of formula 1-9 added, 0.0413 mol of 6-FDA(4,4′-(Hexafluoroisopropylidene)diphthalic anhydride) and 60 g of DEAcwere added and reacted for 48 hours to obtain a polyimide precursorsolution.

<Example 4> 6-FDA/Diamine of Formula 1-10

180 g of DEAc (Diethylacetamide) was charged into a reactor in anitrogen stream, and then 0.0413 mol of the diamine of formula 1-10prepared in Preparative Example 4 was added to dissolve it whilemaintaining the reactor temperature at 25° C. To the solution with thediamine of formula 1-10 added, 0.0413 mol of 6-FDA(4,4′-(Hexafluoroisopropylidene)diphthalic anhydride) and 60 g of DEAcwere added and reacted for 48 hours to obtain a polyimide precursorsolution.

Experimental Example 1

The viscosity of the polyimide precursor solutions and the molecularweight of the polyamic acid prepared in Examples 1 to 4 and ComparativeExample 1 were measured, and the results are shown in Table 1 below.

<Measurement of Viscosity>

The viscosity was measured using Viscotek TDA302.

<Measurement of Molecular Weight>

The molecular weight was measured using Viscotek GPCmax VE2001.

Experimental Example 2

Each of the polyimide precursor solutions prepared in Examples 1 to 4and Comparative Example 1 was spin coated on a glass substrate. Theglass substrate coated with the polyimide precursor solution was placedin an oven, heated at a rate of 5° C./min and cured at 80° C. for 30minutes, at 250° C. for 30 minutes and at 400° C. for 30 to 40 minutesto prepare a polyimide film. Properties of each film were measured, andthe results are shown in Table 1 below.

<Modulus (GPa), Tensile Strength (MPa) and Elongation (%)>

A film of 5 mm×50 mm long and 10 μm thick was stretched at a speed of 10mm/min with a tensile tester (Instron 3342, manufactured by Instron) tomeasure modulus (GPa), tensile strength (MPa) and elongation (%).

TABLE 1 Comparative Example 1 Example 1 Example 2 Example 3 Example 4Diamine used TFMB Formula 1-1 Formula 1-2 Formula 1-9 Formula 1-10 Solidcontent 18.4 17.0 17.1 16.8 16.8 (wt %) Viscosity (cPs) 3500 3890 39103600 3440 Molecular 50,000 73,000 61,000 54,000 55,000 weight (Mw)Curing 5° C./min, 5° C./min, 5° C./min, 5° C./min, 5° C./min, condition 80° C., 30 min  80° C., 30 min  80° C., 30 min  80° C., 30 min  80° C.,30 min 250° C., 30 min 250° C., 30 min 250° C., 30 min 250° C., 30 min250° C., 30 min 400° C., 30 min 400° C., 40 min 400° C., 40 min 400° C.,40 min 400° C., 40 min Film thickness 9.7 9.9 10.8 10.1 9.9 (μm) Modulus(GPa) 2.2 5.0 4.8 4.1 4.2 Tensile 125 138 136 140 141 strength (MPa)Elongation (%) 88 95 90 94 91

As can be seen from the results of Table 1, the polyimide precursorsolution containing the diamine according to the present invention mayhave a viscosity of 3000 cPs or more at a solid content concentration of20% by weight or less, and therefore a polyamic acid having a highermolecular weight was produced compared to Comparative Example 1 usingTFMB. In addition, it can be seen that the polyimide film prepared fromthe polyamic acid having such a high molecular weight has improvedmechanical strength compared to the polyimide film of ComparativeExample 1.

While the present invention has been particularly shown and describedwith reference to specific embodiments thereof, it will be apparent tothose skilled in the art that this specific description is merely apreferred embodiment and that the scope of the invention is not limitedthereby. It is therefore intended that the scope of the invention bedefined by the claims appended hereto and their equivalents.

1. A diamine represented by the formula
 1.

In the formula 1, Z₁ to Z₈ are each independently a carbon atom or anitrogen atom, with the proviso that Z₁ to Z₈ are not nitrogen atoms atthe same time, R₁, R₂, R₃ and R₄ are each independently selected fromthe group consisting of an alkyl group having 1 to 10 carbon atoms, ahaloalkyl group having 1 to 10 carbon atoms, an alkenyl group having 1to 10 carbon atoms, and an aryl group having 6 to 18 carbon atoms, n₁,n₂, n₃ and n₄ are each independently an integer of 0 to 4, and X is asingle bond or a functional group selected from the group consisting ofO, S, S—S, C(═O), —C(═O)O—, CH(OH), S(═O)₂, Si(CH₃)₂, CR′R″, C(═O)NH anda combination thereof, wherein R′ and R″ are each independently selectedfrom the group consisting of a hydrogen atom, an alkyl group having 1 to10 carbon atoms and a fluoroalkyl group having 1 to 10 carbon atoms. 2.The diamine according to claim 1, wherein at least one of Z₁ to Z₄ is acarbon atom, and at least one of Z₅ to Z₈ is a carbon atom.
 3. Thediamine according to claim 1, wherein n₁ and n₂ are each independently0, or R₁ and R₂ are each independently an alkyl group having 1 to 5carbon atoms or a haloalkyl group having 1 to 5 carbon atoms.
 4. Thediamine according to claim 1, wherein Z₁ to Z₄ are all carbon atoms. 5.The diamine according to claim 1, wherein one of Z₁ to Z₄ is a nitrogenatom or one of Z₅ to Z₈ is a nitrogen atom.
 6. The diamine according toclaim 1, wherein one of Z₁ to Z₄ is a nitrogen atom and one of Z₅ to Z₈is a nitrogen atom.
 7. The diamine according to claim 1, wherein X is asingle bond, —O—, —CH₂—, —C(CF₃)—, —C(CH₃)₂—, or —SO₂—.
 8. The diamineaccording to claim 1, wherein the diamine of the formula 1 is selectedfrom compounds of the formulae 1-1 to 1-20:


9. A polyimide precursor comprising a polymerized product of acomposition comprising at least one diamine and at least one aciddianhydride, wherein the diamine comprises the diamine according toclaim
 1. 10. A polyimide film manufactured from the polyimide precursoraccording to claim
 9. 11. A polyimide film manufactured by a methodcomprising: applying a polyimide precursor composition comprising thepolyimide precursor according to claim 9 on a carrier substrate; andheating and curing the polyimide precursor composition.
 12. A flexibledevice comprising the polyimide film according to claim 10 as asubstrate.
 13. A process for producing a flexible display comprising:applying a polyimide precursor composition comprising the polyimideprecursor according to claim 9 on a carrier substrate; heating thepolyimide precursor composition to imidize polyamic acid, therebyforming a polyimide film; forming a device on the polyimide film; andpeeling off the polyimide film on which the device is formed from thecarrier substrate.
 14. The process for producing a flexible displayaccording to claim 13, wherein the process comprises an LTPS (lowtemperature polysilicon) process, an ITO process or an oxide process.15. A method for preparing a diamine having the structure of formula 1,the method comprising the steps of: reacting a compound of the formula(i) with a compound of the formula (ii) to obtain a compound of theformula (iii); reacting the compound of the formula (iii) with acompound of the formula (iv) to obtain a compound of the formula (v);and reducing the compound of the formula (v) to obtain the diamine ofthe formula 1:

wherein, Z_(a) to Z_(a) are each independently a carbon atom or anitrogen atom, with the proviso that Z_(a) to Z_(a) are not nitrogenatoms at the same time, R₁, R₂ and R_(a) are each independently selectedfrom the group consisting of an alkyl group having 1 to 10 carbon atoms,a haloalkyl group having 1 to 10 carbon atoms, an alkenyl group having 1to 10 carbon atoms, and an aryl group having 6 to 18 carbon atoms, n₁,n₂ and n are each independently an integer of 0 to 4, and X is a singlebond or a functional group selected from the group consisting of O, S,S—S, C(═O), —C(═O)O—, CH(OH), S(═O)₂, Si(CH₃)₂, CR′R″, C(═O)NH and acombination thereof, wherein R′ and R″ are each independently selectedfrom the group consisting of a hydrogen atom, an alkyl group having 1 to10 carbon atoms and a fluoroalkyl group having 1 to 10 carbon atoms.